The current methodology for producing mineral oil containing gels includes the use of metal soaps, surfactants (microemulsions), homopolymers, ionic homo- and copolymers and block copolymers. Some common gelling agents for cosmetic oil systems are fatty acid soaps of lithium, calcium, sodium, aluminum, zinc and barium. A number of homo- and copolymers have been used to gel hydrocarbon systems at certain polymer treatment levels including atactic ethylene-propylene. Homopolymers or copolymers which have pendant salt groups also form ion rich aggregates in a non-polar matrix. The ionic interaction and resultant polymer properties of these compositions, however, are dependent on the type of polymer backbone, type of ionic moiety and type of cation. Sulfonated polystyrenes exemplify this kind of system. Surfactant combinations have also been used to gel mineral oil/water systems. Surfactants are used at about 30 wt % to gel oil and to gel 1:4 oil and water mixtures. Nonionic surfactants such as polyoxyethylene sorbitan monoleates exemplify these type of systems.
Block copolymers are also known to form physical cross-links to gels by selective sulfation and subsequent phase separation of a particular block. Block systems including styrene-isoprene, styrene-butadiene and styrene ethylene oxide copolymers have been used for this purpose. For example, U.S. Pat. Nos. 3,867,533, 4,465,663, 4,678,664 and 4,721,579 of BASF disclose aqueous cosmetic gels prepared from polyoxybutylene-polyoxyethylene or polyoxyethylene-polyoxypropylene block copolymers. In addition, the following U.S. Patents disclose compositions which include various cosmetic formulations, some of which contain block polymers:
______________________________________ 3,395,169 Mitchell 1968 3,574,827 Beerbower 1971 3,733,403 Chen 1973 3,928,558 Cheesman et al 1975 4,061,780 Yoshida et al 1977 4,268,502 Martin 1981 4,387,090 Bloich, Jr. 1983 4,673,571 Mahieu et al 1987 4,563,346 Deckner 1986 4,600,030 Newman 1986 4,659,562 Arraudeau et al 1987 ______________________________________
There remains a need in the art for new and improved gels of this type for health and beauty aids such as cosmetics in view of various problems with the prior art vehicles. For example the metal stearates in certain surfactants are potential irritants of the skin. Accordingly, in this invention, new improved and advantageous combinations of block copolymers are provided which produce heterophase thermally reversible mineral oil gels which have desirable properties for applications in the cosmetic and health and beauty aid industry.